One of the lines is going to be acceptable performance. Your phone number formatting microservice is going to be orders of magnitude slower than a client libra

One of the lines is going to be acceptable performance. Your phone number formatting microservice is going to be orders of magnitude slower than a client library. The auth service will likely have to hit a DB anyways. Assuming the microservice call has roughly the same network latency as the DB call and the DB has 0 response time, it would double the total time to perform the auth. It only gets more favorable as DB response times go up. More generally, I think microservices make sense in scenarios where the time to process the request is longer than the network latency incurred by making it a microservice. Things that have to hit a DB are generally okay. Pure functional things that just compute on CPU and RAM are generally not, unless they're very computationally expensive like running a simulation or something like that.